This is a front-end for the Online Encyclopedia of Integer Sequences, made by Christian Perfect. The idea is to provide OEIS entries in non-ancient HTML, and then to think about how they're presented visually. The source code is on GitHub.
%I A206529 #8 Sep 08 2022 08:46:01
%S A206529 11,77,4949,343343,24012401,1680716807,117649117649,823543823543,
%T A206529 57648015764801,4035360740353607,282475249282475249,
%U A206529 19773267431977326743,1384128720113841287201,9688901040796889010407,678223072849678223072849
%N A206529 7^n concatenated with itself.
%H A206529 Vincenzo Librandi, <a href="/A206529/b206529.txt">Table of n, a(n) for n = 0..200</a>
%F A206529 a(n) = A020338(7^n).
%e A206529 a(1)=77 because 7^1 concatenated with 7^1 is 77.
%t A206529 Table[FromDigits[Join[IntegerDigits[7^n],IntegerDigits[7^n]]],{n,0,20}]
%t A206529 #*10^IntegerLength[#]+#&/@(7^Range[0,20]) (* _Harvey P. Dale_, Jul 19 2022 *)
%o A206529 (Magma) [Seqint(Intseq(7^n) cat Intseq(7^n)): n in [0..20]];
%Y A206529 Cf. A000420, A000351, A178664, A206527, A206528.
%K A206529 nonn,base,easy
%O A206529 0,1
%A A206529 _Vincenzo Librandi_, Mar 18 2012